1. Field of the Invention
This invention relates to an electronic control system for an internal combustion engine. Specifically, this invention relates to an electronic system for adjusting a controlled quantity of an internal combustion engine such as a fuel injection rate or a spark timing in response to a property of fuel, for example, the degree of goodness or poorness of vaporization characteristics of fuel.
2. Description of the Prior Art
Since the degree of goodness or poorness of vaporization characteristics of fuel significantly affects the atomization thereof, the air-to-fuel ratio (A/F ratio) of an air-fuel mixture in an internal combustion engine is closely related to the degree of goodness or poorness of vaporization characteristics of fuel. It has been conceived that the degree of goodness or poorness of vaporization characteristics of fuel is detected and the A/F ratio of an air-fuel mixture is corrected in response to the detected degree.
Japanese published unexamined patent application 3-117650 discloses that heavy gasoline is greater in refractive index than regular gasoline, and a gasoline quality sensor detects the refractive index of used gasoline to determine whether or not the used fuel is of a heavy type. Japanese patent application 3-117650 teaches an apparatus for controlling the start of an engine in response to the output signal of the gasoline quality sensor.
Adding alcohol or other material to gasoline changes the refractive index thereof while conditions of atomization thereof are essentially unchanged. Thus, the accuracy of the gasoline quality sensor in Japanese patent application 3-117650 tends to be lowered when alcohol or other material is added to gasoline. In addition, the reliability of an engine control system using such a gasoline quality sensor tends to be decreased when alcohol or other material is added to gasoline.